The size tub depends on the size of the snake. A 6qt is good till they reach around 350 to 400 grams. Then a 15 qt to around 1000 grams, then 32 qt or bigger.I like CB-70 for adults.
The UTH can be taped to the outside bottom of the tub. Be sure to regulate the temp with a reostat or a thermostat.
I like newspaper, use whatever substate you like.Don't forget to add a water dish and at least one hide.
The lid will have to be secured. For a single tub, small bungi cords can work or just some weight on it.
Hope this helps.